Disruption of undecaprenyl phosphate recycling suppresses ampC beta-lactamase induction in Pseudomonas aeruginosa

Abstract

Beta-lactam antibiotics are widely used to treat bacterial infections, but their efficacy is compromised by resistance mechanisms such as the production of beta-lactamases. In Pseudomonas aeruginosa, the chromosomally encoded beta-lactamase AmpC is the primary mediator of beta-lactam resistance. ampC expression is regulated by the transcription factor AmpR, which responds to intracellular peptidoglycan (PG) fragments. Under normal conditions, AmpR binds the PG precursor (UDP-MurNAc-pentapeptide, UDP-M5) and represses ampC expression. However, during beta-lactam treatment or in PG recycling-deficient mutants such as ampD mutants, PG degradation products (anhydromuropeptides, AMP) accumulate and activate AmpR, resulting in elevated ampC expression and beta-lactam resistance. We hypothesized that shifting the balance of PG precursors could modulate AmpR activity and suppress beta-lactamase expression, even in derepressed strains. Undecaprenyl phosphate (UndP) is a lipid carrier essential for translocating PG precursors across the bacterial inner membrane. Recent work has identified members of the DedA superfamily as UndP flippases responsible for recycling this lipid carrier. Disruption of UndP recycling leads to cytoplasmic accumulation of UDP-M5, the known AmpR repressor. Here, we show that deletion of dedA4, which encodes a predicted UndP flippase in P. aeruginosa, causes UDP-M5 accumulation and significantly reduces AmpC production and beta-lactam resistance in an ampD mutant. These findings highlight the influence of PG precursor dynamics on beta-lactamase regulation and identify DedA4 as a promising therapeutic target. Inhibiting UndP recycling offers a novel strategy to counteract beta-lactam resistance in P. aeruginosa and potentially other AmpC-producing pathogens. IMPORTANCEBeta-lactam resistance remains a major clinical challenge, often driven by the overexpression of chromosomally encoded beta-lactamases such as AmpC in Pseudomonas aeruginosa. Strategies to limit ampC activation are urgently needed to preserve the efficacy of these frontline antibiotics. Our study identifies DedA4, a membrane protein involved in undecaprenyl phosphate (UndP) recycling, as a potential target for such intervention. Inactivation of DedA4 disrupts UndP transport, leading to the accumulation of soluble, membrane-unbound PG precursors which act as corepressors of AmpC expression. This disruption in the balance between cell wall synthesis and turnover restores susceptibility to {beta}-lactams, even in strains harboring clinically significant resistance mutations such as those in ampD or dacB. Targeting UndP flippases like DedA4 could therefore represent a novel adjuvant strategy to combat AmpC-mediated beta-lactam resistance.